There isn’t much documentation on how ACF stores values in the DB. Some of us know because we’ve looked. Simple fields that store just text values are saved just like WP custom fields in the DB. More complex fields are not. It really depends on what field types you are using how difficult it will be to get them from GF into ACF. For complex fields you will need to add code that runs when the post is created (see the GF documentation on this) and update the ACF fields.
